1. Field of the Invention
The present invention relates to a projection system, and more particularly, to a highly-efficient single panel digital light processing (DLP) projection system which can be made compact by scrolling color bars using a single scrolling unit and more light efficient by utilizing a low-power low-priced lamp.
2. Description of the Related Art
In general projection systems, a light valve controls the on/off operation of light emitted from a light source on a pixel-by-pixel basis and forms a picture. A magnifying projection unit enlarges the picture to be displayed on a large screen.
A DLP projection system, which uses as a reflective display a DLP panel manufactured using a micro-electro mechanical system (MEMS), is under development.
A DLP panel is manufactured by two-dimensionally arranging a large number of micromirrors corresponding to pixels. The DLP panel turns on or off incident light by independently driving the micromirrors according to image signals corresponding to the pixels and accordingly changing the reflection angle of the incident light, thereby forming a picture.
A general projection system, utilizing such a DLP panel for reflective display, includes a total internal reflection (TIR) prism so that the path of light emitted from an illumination unit and entering the DLP panel is different from that of picture-forming light reflected by the DLP panel.
When the TIR prism is used, incident light is totally reflected by the TIR prism and then illuminates the reflective display. The path of the illuminating light is changed by the reflective display so that the illuminating light advances toward the projection unit. Light advancing toward the projection unit is incident on a total reflection surface of the TIR prism. Since the light is incident upon the total reflection surface of the TIR prism at a small incidence angle, it is directed toward the projection unit without being totally reflected.
Projection systems are classified into either three-panel projection systems or single-panel projection systems, according to the number of light valves used. Three-panel projection systems provide better optical efficiency than single-panel projection systems, but are generally more complicated and expensive. Single-panel projection systems can have a smaller optical system than the three-panel projection systems. However, these single-panel systems provide only ⅓ of the optical efficiency of the three-panel projection systems because red (R), green (G), and blue (B) colors, into which white light is separated, are used sequentially. To be more specific, in a single-panel projection system, white light radiated from a white light source is separated into R, G, and B color beams using color filters, and the three color beams are sequentially sent to a light valve. The light valve operates according to the sequence of color beams received and creates images. As described above, a single-panel projection system uses color beams sequentially, therefore, the light efficiency is reduced to ⅓ the light efficiency of a three-panel projection system.
According to one color scrolling method designed to increase the optical efficiency of a single-panel projection system, white light is separated into R, G, and B color beams, and the three color beams are simultaneously sent to different locations on a light valve. Since an image cannot be produced until all of the R, G, and B color beams reach each pixel of the light valve, the color beams are moved at a constant speed by a color scrolling means.
FIG. 1 illustrates a conventional DLP single panel projection system using a color wheel 103. Referring to FIG. 1, white light emitted from a light source 102 is separated into red (R), green (G), and blue (B) beams by the color wheel 103 in a time sequential manner. The R, G, and B beams pass through a light tunnel 105 so as to have illumination uniformity due to internal multiple reflections. Then, light passed through the light tunnel 105 is made incident upon a TIR prism 135, which is disposed 45 degrees, via a light path changing unit 115. The light path changing unit 115 includes a first reflection mirror 108, a first lens 112, a second reflection mirror 114, and a second lens 117 which are sequentially arranged. The first reflection mirror 108 reflects the light passed through the light tunnel 105. The first lens 112 focuses light reflected by the first reflection mirror 108. The second reflection mirror 114 redirects light passed through the first lens 112 toward the TIR prism 135. The second lens 117 focuses light reflected by the second reflection mirror 114 on the TIR prism 135. Thereafter, the light incident upon the TIR prism 135 illuminates a DLP panel 130 according to the total reflection condition of the TIR prism 135. The DLP panel 130 includes pixels diagonally driven at 45 degrees. This illuminating light is modulated into an image which is magnified by a projection lens 140 and projected onto a screen.
In the DLP single-panel projection system of FIG. 1, the white light emitted from the light source 102 is separated into R, G, and B beams by the color wheel 103 in a time sequential manner, and the R, G, and B beams are focused on the DLP panel 130 to form a picture. Hence, light efficiency is low.
The low light efficiency can be increased by using a high-brightness light source and a high gain screen. However, because a high-brightness lamp usually has a low durability, the use of this lamp shortens the life span of the projection system. Also, the use of a high gain screen narrows a viewing angle.